How many hours of sleep should I be getting?

Well lately I haven’t been sleeping so well and I keep waking up at odd hours of the night and not falling back asleep for awhile. I’m 16 years old, I’m a junior in high school, how many hours of sleep do I need on average to keep me going. It seems that if I sleep more than 9 hours I become very tired during the day, and if I get less than 5 hours, I’m fine till the afternoon. I wake up at 5:45 every morning except for Saturdays and Sundays. I’ve read about sleep deprivation and I’m not showing any signs of it except for the loss of memory. I used to have a photographic memory until 9th grade when I lost my “child” sleeping habits. Getting less sleep i have also noticed an increase in my level of stress. I need some feedback on my sleep.